Field of the Invention
The present invention relates to a method of making aluminum alkyls or alkyl aluminum compounds and especially to the making of trimethylaluminum.
A variety of processes are known for the preparation of aluminum alkyls and for the preparation of trimethylaluminum in particular. Decomposition reactions of aluminum alkyls with alkyl halides are documented in the literature.
One preferred method for making trimethylaluminum involves the sodium reduction of methylaluminum sesquichloride. Such procedure is an expensive one. Processes of this type are described in British Pat. No. 762,200 and U.S. Pat. No. 2,954,389 and in an article by A. V. Grosse and J. M. Mavity, Journal of Organic Chemistry, 5, 106 (1940). Preparation of trimethylaluminum has also been carried out by the sodium reduction of dimethylaluminum chloride as described in an article by S. Pasynkiewicz and M. Boleslawski, Journal of Organometallic Chemistry, 25, 29 (1970). The methods described in the foregoing articles each form a basis for existing commercial processes for the production of trimethylaluminum, but each produce non-usable by-products having limited value in vast quantities in comparison to the trimethylaluminum produced. The by-products produced by the above processes are aluminum and sodium chloride.
The several processes that have utilized the above sodium reduction reactions suffer from an inherent problem in that trimethylaluminum will itself react with sodium to produce sodium tetramethylaluminate, a compound that, unless it reacts with dimethylaluminum chloride will cause reduced yields and present a disposal problem. Sodium tetramethylaluminate is extremely reactive towards moisture in the air, as would excess unreacted sodium. The disposal problems presented by these two compounds represent a significant proportion of the cost of production of trimethylaluminum manufactured by such processes.
Although the conversion of dimethylaluminum chloride to trimethylaluminum without the use of sodium (Cryolite Process) is described in U.S. Pat. No. 2,839,556, this reaction scheme produces a vast amount of solid by-product having limited commercial value.
Two other methods for production of aluminum trialkyls are described in an article by R. Koster and P. Binger, Advances in Inorganic and Radiochemistry, I, 1263 (1965) and by K. S. Pitzer and H. S. Gutowsky, Journal of American Chemical Society, 68, 2204 (1946). Both of these methods suffer from the use of expensive starting materials and the production of non-useful or extremely reactive by-products requiring expensive process equipment and handling techniques.
U.S. Pat. No. 2,744,127 describes a relatively simple process for the preparation of trimethylaluminum which produces as a by-product magnesium chloride in the weight ratio 2.7:1 magnesium chloride:trimethylaluminum. The magnesium chloride has little or no commercial value.
A process for producing a mono-hydrocarbon aluminum dihalide is disclosed in U.S. Pat. No. 2,270,292. In such process, a hydrocarbon halide is reacted with metallic aluminum to form a di-hydrocarbon-aluminum-mono-halide and the latter is then reacted with an aluminum trihalide to form the desired dihalide product.
U.S. Pat. No. 2,863,894 relates to a process for producing aluminum alkyls, wherein aluminum is reacted with a primary alkyl halide, including methyl iodide in the presence of an inert, aromatic-free solvent to form a solution of sesquihalide dissolved in the inert solvent and then reacting the sesquihalide with an alkali metal to form the aluminum alkyl.
A more recent patent, U.S. Pat. No. 4,118,409, provides for jointly making trimethylaluminum and alkylaluminum bromides and iodides by mixing an aluminum trialkyl and a methylaluminum bromide or iodide and then distilling from the mixture trimethylaluminum as a first fraction and then alkylaluminum bromides or iodides as a subsequent fraction. The alkylaluminum halides used in such a redistribution process are themselves expensive compounds.